Sneezing except during the flu is usually symptoms of goodness. Because of the sneezing is a sign of goodness, the one who sneezes must praise Allah. Everyone who hears this must say "Yarhamukallah" that is "Allah have mercy on you". It is one of moralities of Islam. Every muslim must obey this. 

Yawn is a sign that a person's body and spirit are aggravated. It can never be a sign of goodness. For this reason, a Muslim should be able to give up as much as he can. 

The sneezing is a reflection of the yawn. He will come suddenly and be strong. Because of this, the air comes out lungs through the nose and mouth. He brings out air, microbes, and other things along the way. That is why it is natural that sneezing is from the Compassionate, because it has a benefit for the body. The yawn is from the devil, because there is damage to the body.

For this reason, it is necessary to praise to Allah and seek refuge from Allah against the devil.